The beaches are among the highlights of Cancun. There is nearly continuous beach from the town center and along the ~20 km stretch of hotels out to Punta Nizuk. The widest sections are along the 10 km from the Convention Center to Club Med. This is classic beach running, with views to turquoise waters and good packed sand near the water. Tides in this area are not significant, so you won’t find a big difference between times of the day.
Among some of the more popular sections for beach running are: Playa Delfines (across from golf course, very wide), Playa Marlin (near the Westin), and which is located behind Plaza Kukulcan and Playa Forum (wide, but very popular so can get crowded). It’s 5 km between Playa Delfines and Playa Marlin.
The sand is generally firm enough to run with shoes. One can always do one way on the beach and then do the retrun on the main road, which has a sidewalk (but few water views). Note: The entire beach is open to the public — but needs to be accessed from your hotel or from designated access points.